PH Sensor for Arduino,PH0-14 Value Detect Sensor Module + PH Electrode Probe BNC,PH Sensor UNO,PH Sensor for Arduino Kit High quality PH sensor at a convenient price, allows reliable readings easily. The PH for this sensor is not at 0v for a PH7 it's around 2.51v from the multi-meter and PH4 at 3.03. If you calculate the step, 2.51-3.03 =-0.52. The difference between ph4.01 and PH7 is 2.99. The device works perfectly for a variety of applications such as lab work, DIY, test circuits, gardening and fish tank applications, among many others. There is also abundant information on the Internet about its use and codes associated with different applications. The device requires minimal maintenance and cleaning measures, with a protection box, which allows it to be kept in a safe and operational condition for a long time. Color:As Shown Material:Plastic+Metal Package Contents: 1 * PH test module 1 * PH probe